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1508 PD: Management and economics of on-farm pasteurizers

Robert E. James and M. C. Scott Published on 16 October 2008

The goal of a calf-rearing program should be to optimize growth and health while minimizing risk and cost.

Economics of a calf-rearing program should be measured in terms of cost per pound of gain and total cost to rear calves to a given weight/age, including mortality charges.

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As the price of milk replacer ingredients has increased, calf growers have looked towards utilization of unsalable milk from fresh cows and those treated with antibiotics as a source of economical nutrients. However, the practice of feeding raw milk to calves is not recommended due to the potential for disease transmission. Fortunately, pasteurizers have become commercially available that are well-suited to treating the volumes of waste milk found on dairy farms and many calf-raising operations.

The purpose of this [article] is to review the information about calf feeding systems using waste milk, including potential benefits and risks. Recommended protocols for managing uncertainty associated with these feeding systems will be discussed.

Benefits of pasteurized waste milk
Calves fed whole milk grow better than calves fed traditional milk replacers containing 20 percent fat and 20 percent protein. This is due to the higher level of nutrients found in whole milk. (It’s important to note that composition of waste milk can deviate significantly from salable milk). In a study involving over 400 calves, Godden et al. found that calves fed pasteurized waste milk grew 0.26 pounds per day more and also had lower incidence of health problems and mortality than those receiving milk replacer. Differences are probably related to increased nutrient intake by calves fed waste milk. Scott et al. observed that there was no difference in growth of calves fed milk replacers or waste milk on an isocaloric and equal solids basis.

Risks associated with waste milk feeding
Risks include antibiotic and bacterial contamination of waste milk and variations in both the supply and nutrient content of waste milk. Waste milk is comprised of “fresh” cow milk and that from cows treated with antibiotics. The impact of antibiotics on digestive function and antibiotic resistance in calves appears minimal but has not been determined.

Bacterial content of waste milk prior to pasteurization is very variable, ranging from less than 50,000 colony forming units (cfu) per milliliter (cfu/ml) to more than 50 million cfu/ml. Studies in California and Wisconsin have isolated Salmonella, Mycoplasma, E. coli, Mycobacterium and other organisms of concern in raw waste milk. Fortunately, properly operating pasteurizers successfully kill these organisms and are able to reduce standard plate counts (SPC) of waste milk to acceptable levels.

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Waste milk can be a poorly defined liquid in many cases. Studies by Virginia and Wisconsin workers revealed that fat content varied between 1.1 and 11 percent and protein between 2.9 and 4.7 percent depending on number of fresh cows being milked and amount of water added during flushing of milklines at the end of each milking.

In addition to quality concerns, supply of waste milk varies considerably. Blosser estimated that each cow generates between 48 and 136 pounds of waste milk per lactation. In a study of North Carolina and California dairy farms, Scott found that availability of waste milk per calf per day ranged from 5.6 to more than 20 pounds. Dealing with these uncertainties of waste milk supply in a calf-feeding program can be an exceptional management challenge.

Managing the feeding program using pasteurized waste milk
Batch and High Temperature Short Time (HTST) pasteurizers are the most prevalent systems in the U.S. When properly installed and maintained, they will successfully eliminate disease transmission concerns. Pasteurization occurs when milk is held at the recommended temperature for the desired time.

Pasteurization does not sterilize milk! In properly operating systems, a pasteurizer destroys 98 to 99 percent of the bacteria. If pre-pasteurization counts exceed 2,000,000 cfu/ml, a post-pasteurization SPC goal of 20,000 cfu/ml may not be achieved.

Batch pasteurizers operate much the same as a double boiler on a stove top. They must heat and maintain milk at a temperature of 145ºF for 30 minutes. Milk must be agitated to assure that there are no “dead spots” and that the head space above the level of the milk reaches pasteurization temperature as well to assure that milk is not contaminated after pasteurization. Batch systems are generally less expensive and simpler to operate but require manually cleaning.

The HTST units operate similar to the plate cooler in the milking system, except in reverse. They must heat milk to 161ºF for 15 seconds. Their operation and cleaning is more readily automated, and they can process larger volumes of milk more quickly. Temperature is monitored by in-line thermometers and if inadequate the milk can be recirculated through the heat exchanger by use of a diversion valve. These systems are also more expensive and require adequate hot water supplies beyond that used by the milking system.

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It is logical that waste milk be treated with the same care as that given to salable milk, with care given to addressing process control in handling the milk from the cow’s teat until it’s consumed by the calf. The following components and management should be considered essential for maintaining milk quality in the waste milk feeding system:

• Waste milk receiving vessel
Collect and cool waste milk as soon as possible after milking. Holding milk at room temperature in the parlor until the end of milking is not recommended as SPC can exceed several million within a few hours of harvest. If there will be a delay of more than two hours between milking and pasteurization, the waste milk should be cooled.

Recognize that pasteurization of cooled milk increases energy expended and extends time required for pasteurization. Stainless steel or plastic tanks are used to hold waste milk prior to pasteurization. Provisions should be made for cleaning receiving vessels and all lines used to transfer milk each time milk is pasteurized.

• The pasteurizer
Equipment must be installed in accordance with manufacturer’s specifications. In attempting to reduce costs, it’s not uncommon to observe that shortcuts have been taken, such as use of inadequate electrical service or provision of a marginally adequate hot water supply. Adequate hot water (170 to 180ºF) is important for proper operation of HTST units and cleaning and sanitizing of all milk contact surfaces. Closely follow manufacturer’s instructions for operation.

– Recording charts should be used to monitor function and assure that the correct time-temperature was achieved.

– Use a digital thermometer to verify accuracy of the recording thermometer.

– Function is verified by sending samples to a laboratory for measurement of:

• Standard plate count. A reasonable goal is less than 20,000 cfu/ml.

• Alkaline phosphatase. This is an enzyme present in milk, which if properly heated, is destroyed. A reasonable goal is less than 500 million units per milliliter.

• Post-pasteurization
After pasteurization milk should be cooled to 110ºF and fed as soon as possible. If feeding is delayed by more than one hour it should be cooled to less than 40ºF. Vessels receiving pasteurized milk must be cleaned and sanitized. Studies of pasteurizer systems in North Carolina and California revealed that SPC counts can return to levels exceeding 100,000 cfu/ml within one hour of pasteurization if receiving tanks, buckets or bottle are unclean.

• Sanitation of receiving vessels and pasteurizers
All milk contact surfaces should be flushed with potable water after emptying followed by thorough scrubbing with a detergent solution containing sufficient sodium hypochlorite to provide 110 parts per million (PPM) chlorine. Water temperature should be 167ºF. Remove any gaskets and clean by hand. Follow with a potable water rinse and acid sanitizer and drain. Cover all vessels to prevent exposure of milk surfaces to flies and other insects.

– Although cleaning of HTST units can be automated, several important factors should be considered to keep equipment operating to its designed capacity.

• Clean after each use.

• Use cleaners and sanitizers in accordance with manufacturer’s instructions.

• Most machines recommend keeping water temperatures below 180ºF but above 170.

• Once pasteurization is complete immediately begin flushing the system with water until it runs clear. Follow manufacturer instructions which generally recommend cleaning with the alkali detergent for at least 30 minutes, draining and follow with an acid rinse.

• Establish a quality control testing program with a reputable laboratory. During the first month of using the pasteurizer, consider obtaining three samples a day once a week. Measure standard plate count, fat percent, protein percent and total solids for each sample.

– Pre-pasteurization sample to evaluate procedures for obtaining and storing waste milk. SPC above 2,000,000 cfu/ml are unacceptable. Pasteurization can be expected to kill 98 to 99 percent of the organisms, leaving 20,000 cfu/ml. Higher counts indicate excessive holding time at temperatures exceeding 40ºF, unsanitary holding vessels or both.

– Post-pasteurization sample to evaluate efficacy of the pasteurizer. Counts above the 20,000 cfu/ml level indicate problems with the pasteurizer that need to be addressed, such as inadequate temperature or holding time. This may be due to improper programming of the pasteurizer or inadequate hot water supply or clogged plates in the HTST units.

– A sample after the last calf is fed will help evaluate sanitation of bottles, buckets or tanks used to hold or transfer milk to calves. Expect some increase in SPC, but it should remain less than 50,000 cfu/ml. Herds using buckets can expect higher SPC in this sample as feeding typically takes longer than in operations using bottles to feed calves.

– Alkaline phosphatase is an enzyme present in raw milk that is destroyed when the proper temperature-to-time ratio was achieved during pasteurization. This value should be less than 500 million units per milliliter. However, samples with a low value can have SPC exceeding 20,000 cfu/ml.

– Expect costs for these tests to be

• $5 to $10 per sample for SPC

• $7.50 to $10 per sample for alkaline phosphatase

• $2.50 to $5 per sample for fat, protein, lactose and total solids

Managing nutrient content and supply variations of waste milk
Variation in nutrient content and supply of waste milk is a significant challenge of the waste milk-based calf feeding program. Problems with nutrient content are related to the following issues.

• Addition of flush water
After the end of milking, it’s customary to flush the lines with water. The initial milk is similar to whole milk. However, if employees are not careful, significant quantities of flush water can enter the receiving tank, resulting in milk with solids less than 12.5 percent.

• Agitation
When milk is not agitated prior to pasteurization, expect the first milk to be lower in fat than the last milk processed. This can be a problem when milk is directly added to bottles from the pasteurizer.

After pasteurization, milk should be agitated prior to filling buckets. Delays longer than one hour can result in calves fed at the end of the feeding schedule receiving milk with significantly higher fat than those fed initially and vice versa.

• Waste milk supply
Many descriptions of waste milk feeding programs make the assumption that adequate supplies for waste milk are consistently available. Abundant supplies of waste milk could be indicative of a failure in mastitis and herd health control programs, which allow such abundant supplies of treated milk. Blouses noted that the average herd produced between 48 and 136 pounds of waste milk per cow per year.

Scott found that between 5 and 22 pounds of non-salable milk per calf per day was produced on three North Carolina and nine California dairy herds. How does this compare to needs for the calf feeding operation? Waste milk needs are dependent on calf feeding strategies of the farm, which include weaning age and feeding rate.

An additional challenge in utilizing waste milk feeding programs concerns the stability of the daily supply of waste milk. Unfortunately, “averages” can be deceiving. It’s not uncommon to see large fluctuations in the quantity of waste milk available from day to day. Several alternatives exist:

• Use additional salable milk from the bulk tank. This is commonly used when deficiencies in waste milk supply are small. It can be an expensive option when large quantities are required.

• Supplement waste milk by adding additional solids from milk replacer, whey proteins or fat supplements. In some cases, additional water is required as well. This option can be complicated as it requires knowledge of waste milk solids on a daily basis. Total solids can be estimated using digital refractometers, which can provide the basis of recommendations of additional water and milk solids.

• If pasteurizer management is excellent, waste milk is fed to young calves with older calves receiving milk replacer.

• If pasteurizer management is less than desired, milk replacer is fed to the youngest calves with sensitive digestive systems and older calves are fed waste milk.

Scott et al. have shown that when diets contain equal amounts of energy and solids, calves can be successfully switched from waste milk to a higher solids milk replacer or vice versa with little trouble, particularly if calves are more than three weeks old when the switch is made. However, it’s advisable to only make this change once.

Miscellaneous
Pasteurized waste milk feeding systems appear to be most successful when milk is pasteurized twice daily after each milking and just prior to feeding calves. With this system, bacteria don’t have a chance to grow and milk is fresh for the calves. In situations where milk is only pasteurized once daily, it must be cooled to less than 40ºF and then re-warmed to 110ºF prior to feeding. How will this be accomplished? It frequently may be more troublesome than operating the pasteurizer twice daily.

Economics of pasteurized waste milk feeding systems
Determining the cost of a waste milk pasteurizing system is difficult. What is the cost of waste milk? In some parts of the U.S., calf ranches pay $0.25 per gallon for the product and provide trucking from the farm to the calf ranch. Under this scenario the cost is about $3 per hundredweight. However, for those on the home dairy is it really free or at least low in cost? Several scenarios exist to estimate cost of waste milk. They include:

• The cost of production of fresh milk plus costs of operating the pasteurizer unit

• Value of fresh milk

• Cost on the open market (as discussed previously) plus costs of operating the pasteurizer unit

• Assume it’s free

Each scenario has its merits, but it’s not realistic to expect that waste milk is free. This rationale transfers expense for calf feeding to the milking herd, which bears the burden of production cost for “dumped” milk.

Summary
The decision to utilize pasteurized waste milk requires careful consideration on all costs, personnel and health status of the herd. It’s important to remember that the young calf has exacting nutrient requirements and reacts poorly to high levels of undesirable bacteria.

There are many well-designed systems available to producers. Prior to making a decision consider the following:

• How many calves will be fed daily, and what is the average and range in volume of waste milk produced per day? What’s the range in calf numbers per day throughout the year?

• Calculate the total cost of the system to include installation and maintenance, modification of facilities, provision for adequate supplies of hot water for cleaning and adequate storage tanks for pre- and post-pasteurized milk.

• What system has the best service to fix the equipment should there be a breakdown?

• What strategy will be used to supplement waste milk if the supply is inadequate?

• What is health status of the herd? If Johne’s or other diseases are present, there is risk of contaminating calves if there’s a failure of the pasteurizer, which is shown to occur approximately 10 percent of the time in most field studies.

• Do I have the personnel to manage this system correctly?

• Develop a testing program to continuously monitor nutrient content and bacteriological quality of the waste milk to assure that pasteurization is achieved. Fat percent, protein percent, total solids and standard plate count should be evaluated weekly at the beginning and at least monthly thereafter to monitor employees and equipment function. [b:44a0e8194c]PD[/b:44a0e8194c]

References omitted but are available upon request at
—Excerpts from 2007 Professional Dairy Calf and Heifer Growers Association Conference Proceedings

Robert E. James
Professor
Extension Dairy Scientist – Nutrition
Virginia Tech

and

M. C. Scott
Area Dairy Extension Agent
Virginia Cooperative Extension Service

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